1. Field of the Invention
The present invention is in the field of vascular grafting. More particularly, the present invention relates to methods and apparatus for isolation of microvessel cells, generally referred to as endothelial cells, from a patient who is to receive a synthetic graft which has an inner lumenal surface. The microvessel cells are deposited on this inner lumenal surface of the graft.
2. Related Technology
A conventional technology for treating a synthetic or naturally occurring surface with microvessel endothelial cells is set forth in U.S. Pat. No. 4,820,626, issued 11 Apr. 1989 to Stuart K. Williams, et al. In summary, the teaching of this Williams patent is to obtain tissues rich in microvessel endothelial cells, to separate the endothelial cells from the other tissues, and to place these cells onto the inner lumenal surface of the graft.
Recently, technologies for the harvesting, separation, isolation, culturing, and deposition onto a synthetic vascular graft of microvessel endothelial cells have progressed somewhat beyond the labor and skill intensive laboratory methods initially used. Consequently, the time consuming methods which were initially used to prove the efficacy of this technology for reducing the thrombogenicity of synthetic vascular grafts are now practiced with apparatus making the procedure less time consuming, less prone to error, more sterile, and safer for the patient and medical personnel.
Further to the above, a conventional apparatus and method for preparing a synthetic vascular graft with a lumenal lining of endothelial cells taken by liposuction from the patient who is to receive the graft is known in accord with U.S. Pat. No. 5,035,708, issued 30 Jul. 1991, to Paul G. Alchas, et al. According to the Alchas patent, an endothelial cell isolation device includes a primary chamber tapering downwardly to a secondary chamber or ampule. The secondary chamber also has an upper inlet port and a lower outlet port communicating outwardly of the cell isolation device. Digested fat tissue slurry, with microvessel endothelial cells therein, is introduced into the upper primary chamber, and the isolation device is centrifuged at about 700 G for about 7 minutes to produce an endothelial cell product in the form of a "pellet" composed essentially of endothelial cells. This pellet of endothelial cells is then isolated from the fat cells and red blood cells also in the chamber of the isolation device, and is transferred from the cell isolation device to a cell deposition apparatus. This cell deposition apparatus effects dispersal of the endothelial cells in a solution of autologous serum and media. From this suspension, the endothelial cells are deposited on the inner lumenal surface of a synthetic vascular graft.
However, with a cell isolation device of the type taught by the Alchas patent, the relative inefficiency of washing of the slurry to remove free fat therefrom, in combination with the inefficiency of separation of the microvessel endothelial cells from the fat cells in the slurry means that a low yield of endothelial cells is provided with which to do the cell deposition onto the synthetic graft. As a result, many microvessel endothelial cells which are present in the fat slurry are simply not recovered and are thrown away with the disposable device. Consequently, the patient may have to endure a more extensive liposuction than otherwise would be required in order to provide a sufficient number of endothelial cells.
Yet another conventional apparatus for isolating the microvessel endothelial cells present in a fat slurry is known in accord with European Patent Application No. 92303973.9, having a Publication No. 512,769, and a publication date of Nov. 11, 1992. According to the identified publication, a singular processing vessel is utilized to receive fat removed from a patient by liposuction, to rinse this fat, to digest the fat product in order to free the microvessel endothelial cells, and to isolate these endothelial cells from the fat cells and other materials present in the vessel. The endothelial cells so isolated are then transferred from the processing vessel to a graft deposition device for deposition on the inner lumenal surface of the synthetic graft. The conventional teaching is to employ a metallic screen partition or screen basket to define a fat-receiving and rinsing chamber. However, as is explained below, it appears as if the surface energy or electro-chemical activity of the metallic mesh screen material is itself detrimental to microvessel cells.
However, a need exists to improve the yield of viable endothelial cells recovered from a fat specimen taken from a patient preparatory to implantation of a synthetic graft. That is, the endothelial cells which are present in the fat specimen should be more efficiently separated from the fat cells, blood cells, connective tissues, and other materials which are present in the specimen, so that a larger number of such endothelial cells are available to be deposited onto the synthetic graft.
Additionally, a need exists to improve the safety, efficiency in terms of time and skills required and in terms of yield of microvessel cells available for deposition on the graft, manufacturability, and user convenience of the available apparatus for separating, and isolating endothelial microvessel cells for use on the vascular graft. In other words, the entire procedure should be made less of a laboratory-like procedure requiring highly skilled personnel, make-shift apparatus, and considerable time delays; and into a procedure which can be accomplished with little specialized training, in a short time while the graft implantation surgery is underway, and with high sterility and safety for both the patient and the surgical personnel.